Molecular volume-controlled shape-selective catalysis for synthesis of cinnamate over microporous zeolites

On account of the safety and environmental problems arose from the inorganic acids use in the traditional cinnamate synthesis technology, developing eco-friendly solid-acid catalysts with low cost, high efficiency and recyclability is indispensable in cinnamate synthesis. Due to the unique shape-selective catalysis and diverse acidic properties of microporous zeolites, three different solid acid formulations including H-ZSM-5, H-Y and H-8 are selected as catalysts and applied in catalytic synthesis of cinnamate. The effect of acidic property and pore structure on the performance of esterification of cinnamic acid with alcohols is emphatically investigated for three different zeolites after optimizing the catalytic reaction conditions. H-8 zeolite exhibits the highest catalytic activity among three zeolites in the esterification of cinnamic acid with ethanol, owing to its strongest acidic property and largest pore channel. Taking account of the different structural properties of three microporous zeolites, it is considered that the pore size plays a dominant role in the synthesis of cinnamate. Furthermore, H-8 zeolite always shows the highest catalytic activity coupled with the outstanding recyclability and regeneration efficiency, even in the condition of different alcohols used in cinnamate esterification reaction. It is found that the conversion of cinnamic acid is closely related to the molecular volume of intermediates and product molecules from experiment data and theoretical calculation. Specifically, the smaller molecular volume of intermediates and product molecules inclines to obtain the higher conversion of cinnamic acid and vice versa, which can be well explained from the perspective of mass transfer efficiency. It demonstrates that the activity of esterification reaction for cinnamic acid over H-8 zeolite is dominantly associated with molecular volume of intermediates and product molecules. The research work provides a successful paradigm for microporous zeolite in shape-selective catalytic synthesis of cinnamate controlled by molecular volume.